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            "title": "Copy List with Random Pointer",
            "titleSlug": "copy-list-with-random-pointer",
            "content": "<p>A linked list of length <code>n</code> is given such that each node contains an additional random pointer, which could point to any node in the list, or <code>null</code>.</p>\n\n<p>Construct a <a href=\"https://en.wikipedia.org/wiki/Object_copying#Deep_copy\" target=\"_blank\"><strong>deep copy</strong></a> of the list. The deep copy should consist of exactly <code>n</code> <strong>brand new</strong> nodes, where each new node has its value set to the value of its corresponding original node. Both the <code>next</code> and <code>random</code> pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. <strong>None of the pointers in the new list should point to nodes in the original list</strong>.</p>\n\n<p>For example, if there are two nodes <code>X</code> and <code>Y</code> in the original list, where <code>X.random --&gt; Y</code>, then for the corresponding two nodes <code>x</code> and <code>y</code> in the copied list, <code>x.random --&gt; y</code>.</p>\n\n<p>Return <em>the head of the copied linked list</em>.</p>\n\n<p>The linked list is represented in the input/output as a list of <code>n</code> nodes. Each node is represented as a pair of <code>[val, random_index]</code> where:</p>\n\n<ul>\n\t<li><code>val</code>: an integer representing <code>Node.val</code></li>\n\t<li><code>random_index</code>: the index of the node (range from <code>0</code> to <code>n-1</code>) that the <code>random</code> pointer points to, or <code>null</code> if it does not point to any node.</li>\n</ul>\n\n<p>Your code will <strong>only</strong> be given the <code>head</code> of the original linked list.</p>\n\n<p>&nbsp;</p>\n<p><strong>Example 1:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2019/12/18/e1.png\" style=\"width: 700px; height: 142px;\" />\n<pre>\n<strong>Input:</strong> head = [[7,null],[13,0],[11,4],[10,2],[1,0]]\n<strong>Output:</strong> [[7,null],[13,0],[11,4],[10,2],[1,0]]\n</pre>\n\n<p><strong>Example 2:</strong></p>\n<img alt=\"\" src=\"https://assets.leetcode.com/uploads/2019/12/18/e2.png\" style=\"width: 700px; height: 114px;\" />\n<pre>\n<strong>Input:</strong> head = [[1,1],[2,1]]\n<strong>Output:</strong> [[1,1],[2,1]]\n</pre>\n\n<p><strong>Example 3:</strong></p>\n\n<p><strong><img alt=\"\" src=\"https://assets.leetcode.com/uploads/2019/12/18/e3.png\" style=\"width: 700px; height: 122px;\" /></strong></p>\n\n<pre>\n<strong>Input:</strong> head = [[3,null],[3,0],[3,null]]\n<strong>Output:</strong> [[3,null],[3,0],[3,null]]\n</pre>\n\n<p>&nbsp;</p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>0 &lt;= n &lt;= 1000</code></li>\n\t<li><code>-10<sup>4</sup> &lt;= Node.val &lt;= 10<sup>4</sup></code></li>\n\t<li><code>Node.random</code> is <code>null</code> or is pointing to some node in the linked list.</li>\n</ul>\n",
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                    "name": "Hash Table",
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                    "code": "/*\n// Definition for a Node.\nclass Node {\npublic:\n    int val;\n    Node* next;\n    Node* random;\n    \n    Node(int _val) {\n        val = _val;\n        next = NULL;\n        random = NULL;\n    }\n};\n*/\n\nclass Solution {\npublic:\n    Node* copyRandomList(Node* head) {\n        \n    }\n};",
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                    "code": "/*\n// Definition for a Node.\nclass Node {\n    int val;\n    Node next;\n    Node random;\n\n    public Node(int val) {\n        this.val = val;\n        this.next = null;\n        this.random = null;\n    }\n}\n*/\n\nclass Solution {\n    public Node copyRandomList(Node head) {\n        \n    }\n}",
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                    "lang": "Python",
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                    "code": "\"\"\"\n# Definition for a Node.\nclass Node:\n    def __init__(self, x, next=None, random=None):\n        self.val = int(x)\n        self.next = next\n        self.random = random\n\"\"\"\n\nclass Solution(object):\n    def copyRandomList(self, head):\n        \"\"\"\n        :type head: Node\n        :rtype: Node\n        \"\"\"\n        ",
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                    "code": "\"\"\"\n# Definition for a Node.\nclass Node:\n    def __init__(self, x: int, next: 'Node' = None, random: 'Node' = None):\n        self.val = int(x)\n        self.next = next\n        self.random = random\n\"\"\"\n\nclass Solution:\n    def copyRandomList(self, head: 'Optional[Node]') -> 'Optional[Node]':\n        ",
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                    "lang": "C",
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                    "code": "/**\n * Definition for a Node.\n * struct Node {\n *     int val;\n *     struct Node *next;\n *     struct Node *random;\n * };\n */\n\nstruct Node* copyRandomList(struct Node* head) {\n\t\n}",
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                    "code": "/*\n// Definition for a Node.\npublic class Node {\n    public int val;\n    public Node next;\n    public Node random;\n    \n    public Node(int _val) {\n        val = _val;\n        next = null;\n        random = null;\n    }\n}\n*/\n\npublic class Solution {\n    public Node CopyRandomList(Node head) {\n        \n    }\n}",
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                    "lang": "JavaScript",
                    "langSlug": "javascript",
                    "code": "/**\n * // Definition for a Node.\n * function Node(val, next, random) {\n *    this.val = val;\n *    this.next = next;\n *    this.random = random;\n * };\n */\n\n/**\n * @param {Node} head\n * @return {Node}\n */\nvar copyRandomList = function(head) {\n    \n};",
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                    "code": "# Definition for Node.\n# class Node\n#     attr_accessor :val, :next, :random\n#     def initialize(val = 0)\n#         @val = val\n#\t\t  @next = nil\n#\t\t  @random = nil\n#     end\n# end\n\n# @param {Node} node\n# @return {Node}\ndef copyRandomList(head)\n    \nend",
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                    "lang": "Swift",
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                    "code": "/**\n * Definition for a Node.\n * public class Node {\n *     public var val: Int\n *     public var next: Node?\n *     public var random: Node?\n *     public init(_ val: Int) {\n *         self.val = val\n *         self.next = nil\n *    \t   self.random = nil\n *     }\n * }\n */\n\nclass Solution {\n    func copyRandomList(_ head: Node?) -> Node? {\n        \n    }\n}",
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                {
                    "lang": "Go",
                    "langSlug": "golang",
                    "code": "/**\n * Definition for a Node.\n * type Node struct {\n *     Val int\n *     Next *Node\n *     Random *Node\n * }\n */\n\nfunc copyRandomList(head *Node) *Node {\n    \n}",
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                    "code": "/**\n * Definition for a Node.\n * class Node(var _value: Int) {\n *   var value: Int = _value\n *   var next: Node = null\n *   var random: Node = null\n * }\n */\n\nobject Solution {\n    def copyRandomList(head: Node): Node = {\n        \n    }\n}",
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                    "lang": "Kotlin",
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                    "code": "/**\n * Example:\n * var ti = Node(5)\n * var v = ti.`val`\n * Definition for a Node.\n * class Node(var `val`: Int) {\n *     var next: Node? = null\n *     var random: Node? = null\n * }\n */\n\nclass Solution {\n    fun copyRandomList(node: Node?): Node? {\n        \n    }\n}",
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                    "lang": "PHP",
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                    "code": "/**\n * Definition for a Node.\n * class Node {\n *     public $val = null;\n *     public $next = null;\n *     public $random = null;\n *     function __construct($val = 0) {\n *         $this->val = $val;\n *         $this->next = null;\n *         $this->random = null;\n *     }\n * }\n */\n\nclass Solution {\n    /**\n     * @param Node $head\n     * @return Node\n     */\n    function copyRandomList($head) {\n        \n    }\n}",
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                {
                    "lang": "TypeScript",
                    "langSlug": "typescript",
                    "code": "/**\n * Definition for Node.\n * class Node {\n *     val: number\n *     next: Node | null\n *     random: Node | null\n *     constructor(val?: number, next?: Node, random?: Node) {\n *         this.val = (val===undefined ? 0 : val)\n *         this.next = (next===undefined ? null : next)\n *         this.random = (random===undefined ? null : random)\n *     }\n * }\n */\n\nfunction copyRandomList(head: Node | null): Node | null {\n    \n};",
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            "hints": [
                "Just iterate the linked list and create copies of the nodes on the go. Since a node can be referenced from multiple nodes due to the random pointers, make sure you are not making multiple copies of the same node.",
                "You may want to use extra space to keep <b>old node ---> new node</b> mapping to prevent creating multiples copies of same node.",
                "We can avoid using extra space for old node ---> new node mapping, by tweaking the original linked list. Simply interweave the nodes of the old and copied list. \r\nFor e.g.\r\n<pre>\r\nOld List: A --> B --> C --> D\r\nInterWeaved List: A --> A' --> B --> B' --> C --> C' --> D --> D'\r\n</pre>",
                "The interweaving is done using <b>next</b> pointers and we can make use of interweaved structure to get the correct reference nodes for <b>random</b> pointers."
            ],
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Java 8 features such as lambda expressions and stream API can be used. </p>\\r\\n\\r\\n<p>Most standard library headers are already included automatically for your convenience.</p>\\r\\n<p>Includes <code>Pair</code> class from https://docs.oracle.com/javase/8/javafx/api/javafx/util/Pair.html.</p>\"], \"python\": [\"Python\", \"<p><code>Python 2.7.12</code>.</p>\\r\\n\\r\\n<p>Most libraries are already imported automatically for your convenience, such as <a href=\\\"https://docs.python.org/2/library/array.html\\\" target=\\\"_blank\\\">array</a>, <a href=\\\"https://docs.python.org/2/library/bisect.html\\\" target=\\\"_blank\\\">bisect</a>, <a href=\\\"https://docs.python.org/2/library/collections.html\\\" target=\\\"_blank\\\">collections</a>. If you need more libraries, you can import it yourself.</p>\\r\\n\\r\\n<p>For Map/TreeMap data structure, you may use <a href=\\\"http://www.grantjenks.com/docs/sortedcontainers/\\\" target=\\\"_blank\\\">sortedcontainers</a> library.</p>\\r\\n\\r\\n<p>Note that Python 2.7 <a href=\\\"https://www.python.org/dev/peps/pep-0373/\\\" target=\\\"_blank\\\">will not be maintained past 2020</a>. For the latest Python, please choose Python3 instead.</p>\"], \"c\": [\"C\", \"<p>Compiled with <code>gcc 8.2</code> using the gnu99 standard.</p>\\r\\n\\r\\n<p>Your code is compiled with level one optimization (<code>-O1</code>). <a href=\\\"https://github.com/google/sanitizers/wiki/AddressSanitizer\\\" target=\\\"_blank\\\">AddressSanitizer</a> is also enabled to help detect out-of-bounds and use-after-free bugs.</p>\\r\\n\\r\\n<p>Most standard library headers are already included automatically for your convenience.</p>\\r\\n\\r\\n<p>For hash table operations, you may use <a href=\\\"https://troydhanson.github.io/uthash/\\\" target=\\\"_blank\\\">uthash</a>. \\\"uthash.h\\\" is included by default. Below are some examples:</p>\\r\\n\\r\\n<p><b>1. Adding an item to a hash.</b>\\r\\n<pre>\\r\\nstruct hash_entry {\\r\\n    int id;            /* we'll use this field as the key */\\r\\n    char name[10];\\r\\n    UT_hash_handle hh; /* makes this structure hashable */\\r\\n};\\r\\n\\r\\nstruct hash_entry *users = NULL;\\r\\n\\r\\nvoid add_user(struct hash_entry *s) {\\r\\n    HASH_ADD_INT(users, id, s);\\r\\n}\\r\\n</pre>\\r\\n</p>\\r\\n\\r\\n<p><b>2. Looking up an item in a hash:</b>\\r\\n<pre>\\r\\nstruct hash_entry *find_user(int user_id) {\\r\\n    struct hash_entry *s;\\r\\n    HASH_FIND_INT(users, &user_id, s);\\r\\n    return s;\\r\\n}\\r\\n</pre>\\r\\n</p>\\r\\n\\r\\n<p><b>3. Deleting an item in a hash:</b>\\r\\n<pre>\\r\\nvoid delete_user(struct hash_entry *user) {\\r\\n    HASH_DEL(users, user);  \\r\\n}\\r\\n</pre>\\r\\n</p>\"], \"csharp\": [\"C#\", \"<p><a href=\\\"https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-9\\\" target=\\\"_blank\\\">C# 10 with .NET 6 runtime</a></p>\\r\\n\\r\\n<p>Your code is compiled with debug flag enabled (<code>/debug</code>).</p>\"], \"javascript\": [\"JavaScript\", \"<p><code>Node.js 16.13.2</code>.</p>\\r\\n\\r\\n<p>Your code is run with <code>--harmony</code> flag, enabling <a href=\\\"http://node.green/\\\" target=\\\"_blank\\\">new ES6 features</a>.</p>\\r\\n\\r\\n<p><a href=\\\"https://lodash.com\\\" target=\\\"_blank\\\">lodash.js</a> library is included by default.</p>\\r\\n\\r\\n<p>For Priority Queue / Queue data structures, you may use <a href=\\\"https://github.com/datastructures-js/priority-queue\\\" target=\\\"_blank\\\">datastructures-js/priority-queue</a> and <a href=\\\"https://github.com/datastructures-js/queue\\\" target=\\\"_blank\\\">datastructures-js/queue</a>.</p>\"], \"ruby\": [\"Ruby\", \"<p><code>Ruby 3.1</code></p>\\r\\n\\r\\n<p>Some common data structure implementations are provided in the Algorithms module: https://www.rubydoc.info/github/kanwei/algorithms/Algorithms</p>\"], \"swift\": [\"Swift\", \"<p><code>Swift 5.5.2</code>.</p>\"], \"golang\": [\"Go\", \"<p><code>Go 1.17.6</code>.</p>\\r\\n\\r\\n<p>Support <a href=\\\"https://godoc.org/github.com/emirpasic/gods\\\" target=\\\"_blank\\\">https://godoc.org/github.com/emirpasic/gods</a> library.</p>\"], \"python3\": [\"Python3\", \"<p><code>Python 3.10</code>.</p>\\r\\n\\r\\n<p>Most libraries are already imported automatically for your convenience, such as <a href=\\\"https://docs.python.org/3/library/array.html\\\" target=\\\"_blank\\\">array</a>, <a href=\\\"https://docs.python.org/3/library/bisect.html\\\" target=\\\"_blank\\\">bisect</a>, <a href=\\\"https://docs.python.org/3/library/collections.html\\\" target=\\\"_blank\\\">collections</a>. If you need more libraries, you can import it yourself.</p>\\r\\n\\r\\n<p>For Map/TreeMap data structure, you may use <a href=\\\"http://www.grantjenks.com/docs/sortedcontainers/\\\" target=\\\"_blank\\\">sortedcontainers</a> library.</p>\"], \"scala\": [\"Scala\", \"<p><code>Scala 2.13.7</code>.</p>\"], \"kotlin\": [\"Kotlin\", \"<p><code>Kotlin 1.3.10</code>.</p>\"], \"php\": [\"PHP\", \"<p><code>PHP 8.1</code>.</p>\\r\\n<p>With bcmath module</p>\"], \"typescript\": [\"Typescript\", \"<p><code>TypeScript 4.5.4, Node.js 16.13.2</code>.</p>\\r\\n\\r\\n<p>Your code is run with <code>--harmony</code> flag, enabling <a href=\\\"http://node.green/\\\" target=\\\"_blank\\\">new ES2020 features</a>.</p>\\r\\n\\r\\n<p><a href=\\\"https://lodash.com\\\" target=\\\"_blank\\\">lodash.js</a> library is included by default.</p>\"]}",
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